An operator propelled and/or guided portable trencher is disclosed having a wheeled carriage with an operator manipulable handle bar mounted thereat. The carriage includes a wheel mounting base assembly and a drive frame assembly pivotably connected to each other. A trenching chain assembly is mounted to the drive frame assembly and has a chain maintained at a multi-sprocket chain guide. One sprocket of the chain guide is movably mounted and biased to tension the chain while allowing sprocket movement to partially relieve chain tension during chain use in case of debris entrainment at the chain. An operator manipulable support is connected with the mounting base assembly and is engageable at structure at the drive frame assembly providing operator selection of pivotable location of the drive frame assembly relative to the wheel mounting base assembly during trencher storage and use.